The Surprising Reason Why First-Born Children Are More Likely to Be Nearsighted

By 2050, scientists predict about half the world's population will be nearsighted. Also known as myopia, nearsightedness has reached epidemic levels worldwide, and researchers have pointed to one surprising reason: helicopter parenting.

In a study published in JAMA Opthomology, researchers at Cardiff University in Wales used data from the British Biobank longitudinal study, which took information from 90,000 adults between age 40 and 69. They combined information about people's lifestyles and medical history and found that first-born children were 10 percent more likely to be nearsighted, and 20 percent more likely to be severely nearsighted. The risk then gets lower and lower with descending birth order. But when they adjusted for level of education, that connection basically went away.

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What does education have to do with it? It's all about parental investment. First-born children tend to have more pressure placed on them to succeed, and tend to spend a longer amount of time in school than their younger siblings. NPR notes that high income, education and less time spent outdoors contribute to myopia, and that's long been the stereotype of the oldest child: the overachieving bookworm who must succeed while younger siblings run around unsupervised.

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Because the study was observational, the researchers say they can't definitively conclude that spending more time studying inside instead of playing outside directly causes nearsightedness. (After all, genetics play a role, too.) But doing "near" work like reading books and looking at screens can lead to myopia, so the connection to education makes sense. "My assumption is that individuals who go on to spend more years in full-time education spend relatively less time outdoors and relatively more time in tasks such as reading during their childhood," lead author Jeremy Guggenheim, PhD, told Time.